As disclosed in Korean Patent Registration Publication No. 10-0548310 (which will be referred to as Patent Document 1), a conventional washing machine includes: an outer case forming an outer shape; an outer tub which is supported on an inside of the outer case and receives wash water therein; an inner tub which is rotatably accommodated in an inside of the outer tub and is used for both washing and dehydrating; a pulsator which is mounted relatively rotatably in an inside of the inner tub, to thus form a washing water flow; a drive motor for generating a driving force for rotating the inner tub and the pulsator; an inner tub rotating shaft which receives the driving force of the drive motor thereby rotating the inner tub; a pulsator rotating shaft which receives the driving force of the drive motor thereby rotating the pulsator; a sun gear which is connected to the drive motor and is connected to the pulsator rotating shaft; a plurality of planetary gears which are simultaneously engaged with both the sun gear and a ring gear; a carrier supporting the planetary gears so as to be rotated and revolved; and a clutch spring for controlling the rotation of the inner tub and the pulsator during washing or dehydrating.
The conventional washing machine disclosed in Patent Document 1 has a planetary gear set including the sun gear, the ring gear, the planetary gears and the carrier, and reduces the rotational force of the drive motor, to then be transferred to the pulsator and the inner tub, and operates the clutch spring to selectively transmit power to the pulsator and the inner tub, to thus rotate only the pulsator during washing or to thus rotate both the pulsator and the inner tub simultaneously during dehydrating.
However, the conventional washing machine needs the planetary gear set and the clutch in order to selectively rotate the pulsator and the inner tub, to accordingly cause the configuration of the conventional washing machine to be complicated and the production cost thereof to increase.
Further, since the conventional washing machine is configured to have the planetary gear set and the clutch spring between the drive motor and the outer tub, the space occupied in the height direction of the washing machine is increased and thus the height of the washing machine increases. Otherwise, since the height of the inner tub should be reduced in an identical height of the washing machine, there is a problem that a washing capacity is reduced.
Furthermore, when the pulsator rotating shaft is rotated in only one direction where the clutch spring is compressed upon dehydration of the conventional washing machine, the clutch spring is tightened to the outer peripheral surfaces of a first clutch drum and a second clutch drum, whereby the pulsator rotating shaft and the inner tub rotating shaft are integrally rotated in an identical direction at an identical speed by the tension of the clutch spring. In this case, conventionally, a bearing rotatable only in one direction is used as a bearing for supporting the planetary gear set.
As a result, since the conventional washing machine disclosed in Patent Document 1 has a structure that the pulsator and the inner tub may be rotated only in an identical direction, but may not be rotated in opposite directions to each other, there is a problem that a variety of wash water flows may not be formed and there is a limit to improve performance of the washing machine.
In addition, another conventional washing machine motor is configured to rotate only the pulsator in a state of braking the inner tub during washing and to rotate both the pulsator and the inner tub at the same time during dehydrating.
Meanwhile, Korean Patent Application Publication No. 10-2012-0136081 (which will be referred to as Patent Document 2) disclosed a driving apparatus for a direct drive type washing machine, the driving apparatus including: a dehydrating tank rotating shaft which is rotatably supported on a support member and is connected to a dehydrating tank, to thus rotate the dehydrating tank; a pulsator rotating shaft which is rotatably disposed in an inside of the dehydrating tank rotating shaft and is connected to a pulsator, to thus rotate the pulsator; an inner rotor which is connected to the dehydrating tank rotating shaft; an outer rotor which is connected to the pulsator rotating shaft; and a double stator which is disposed with an air gap between the inner rotor and the outer rotor, to thereby form a magnetic circuit together with each of the inner rotor and the outer rotor.
However, the driving apparatus disclosed in Patent Document 2 is configured to rotate the dehydrating tank through the dehydrating tank rotating shaft by the inner rotor, and to rotate the pulsator by the pulsator rotating shaft by the outer rotor. Thus, the inner rotor is designed to have a high-speed, low-torque characteristic of about 1000 rpm and 3 Nm to fit a dehydration mode, and the outer rotor is designed to have a low-speed, high-torque characteristic of about 100 rpm and 15 Nm to fit a washing mode.
Thus, when the pulsator and the washing tub are intended to be driven in opposite directions to each other by rotating the inner rotor and the outer rotor in opposite directions to each other so as to form various water flow patterns in a washing mode, and since the inner rotor is designed to have a high-speed, low-torque characteristic in the washing mode, there occurs a problem that the torque is small and the current is increased in the case that the inner rotor is applied to the washing mode. In particular, since the washing machine having the washing capacity of a 8 Kg class is required to have a high-torque of 15 Nm or so, and the washing machine of the washing capacity of a 13 Kg class is required to have a high-torque of 40 Nm or so, a large-capacity washing machine of the 8 Kg class or higher has a problem of a temperature rise due to a current density increase with decreased efficiency.